EP-0 968 039 B1 discloses a backflush filter device for use of slotted hole screen tubular filter elements which can be accommodated in a housing with a filter inlet and an outlet for the fluid to be filtered. Flow through the filter elements for filtration or backflushing is possible in both directions. For backflushing, a drivable flushing arm has a fluid outlet for fouled fluid and can be moved in succession under the flow cross sections of the filter elements. In the known solution, at least some of the inserted slotted hole screen tubular filter elements are made conical. The structural length of the conical filter elements is at least ten times greater than the largest existing passage cross section for the fluid. The distance between the individual conical slotted hole screen tubular filter elements or between them and the cylindrical ones in the direction of their free ends is enlarged, with the result that the outflow space in the filter housing is enlarged, and moreover the escape resistance in filter operation is lowered. During backflushing, the conical slotted hole screen tube filter element presents a clear advantage over the cylindrical one, primarily due to the relatively larger exit cross section of the conical filter elements compared to the cylindrical ones for the same filter surface. Since the exit cross section for the conical filter elements is comparatively small relative to the entry cross section formed by the filter surface, that is, the free element surface, depending on the magnitude of the flow resistance of the slotted tube, a bottleneck forms in a large part of the system pressure drops off. Therefore, in the known solution small pressure losses occur, having a beneficial effect in terms of energy during backflushing.
During backflushing a large part of the volumetric throughput for conical and cylindrical filter elements is achieved fundamentally on the lower filter end. The volumetric flows decrease very quickly. The conical element is backflushed much farther. Also, the velocity gradient is less. With incorporation of the velocity profiles relative to the filter surface, an additional cleaning effect compared to cylindrical elements due to the conicity of the element is caused. This additional cleaning effect takes place carefully due to the essentially constant velocity attained when the conical filter elements are being cleaned off, prolonging the service life of these filter elements.
DE 40 30 084 A1 discloses a backflushing device can be backflushed with the dirty liquid is to be filtered, preferably in counterflow to the filtering direction. The known solution in the filter housing has a plurality of filter cells in a circular configuration can be connected to the sludge discharge using a flushing arm driven by a rotary drive individually or in small groups for backflushing. Although, in the known configuration in the backflushing process, the dirty liquid flows through the filter cells with a high turbulent velocity in the longitudinal direction and in the process dissolves and removes the deposited contaminants, the filtering and backflushing result can be improved. Since the filter elements are made cylindrical, they are located tightly next to one another in the filter housing and the free discharge space in the filter housing is accordingly small. In normal filter operation, the outflow resistance for the filtered fluid is then increased by the mutual influence of the cylindrical filter elements on one another. Accordingly, the pressure difference between the filter inlet and outlet is also increased, leading to an altogether poor energy balance in the described known solution.
Even if, as described in DE 83 06 970 U, the cylindrical filter elements are located at a clear distance from one another within the filter housing, especially during backflushing of these cylindrical filter elements a nonuniform fluid flow results, with the consequence that the fluid speed continuously increases within the cylindrical elements. This fluid flow likewise adversely affects the energy balance of the entire backflushing device.
DE 38 12 876 A1 discloses a conical filter element used for filtering and separating different substances and particles. A conically wound wire in the form of a helix or a helical cone is routed within support rods run onto one another. The penetrated conical construction in which the length-width ratio is in the range of 1 produces a type of funnel effect intended to enhance the separation performance. Even if the pertinent conical filtering and separating element were used in a backflushing device, in any case a larger exit cross section for the fluid relative to the entry cross section formed by the filter surface would not be achieved. Thus, increased flow resistances arise adversely affect the efficiency during backflushing. A device comparable to this arrangement is also disclosed by U.S. Pat. No. 2,237,964.
When the conical or cylindrical filter elements according to the above described prior art and the pertinent backflushing devices are used for filtration tasks, in ferritic portions can be found as contaminants in the fluid flow to a high degree, is for example often the case in cooling lubricant fluids are to be filtered, the described known solutions however reach their performance limits. They do filter the ferritic portions out of the fluid flow. The free filter pores of the respective filtration material used however quickly clog with the ferritic portions so that soon the filtration part of the respective filter element is blocked, regardless of whether it is made conical or cylindrical. Even if these filter elements are then used in backflushing filter devices in which counterflushing the respective filter element in the opposite throughflow direction from the clean side to clean off the filtration part is possible, the pertinent cleaning processes must then be undertaken exceptionally often. This requirement adversely affects the filtration performance of the respective device. On the other hand, agglutination or caking of the ferritic portions with the filter material of the filtration part often occurs. During backflushing, the ferritic contamination may also then remain joined to other contaminant portions in the filtration part, or damage to the filtration part occurs during backflushing, especially on its filtration layer or the slotted hole screen tube material of the filter element.
FR-2 718 065 A1 discloses a generic filter element removes contaminants from the fluid as throughflow proceeds from the inside to the outside. In the filter element with its cylindrical mat structure, there are two rod-shaped permanent magnets which trap magnetizable, especially ferritic portions, out of the fluid as it flows through the filter element. To remove the captured ferritic portions from the rod-like permanent magnets, a stripping plate encloses the rod-like permanent magnets on the outer circumferential side and is configured to be able to move within the filter element space by a hydraulic or pneumatic cylinder to clean-off in the direction of motion from top to bottom in the position of use of the filter element. The discharge of the ferritic portions takes place on the bottom of the filtration part held in the housing. After clean-off in the form of stripping, the working cylinder resets the stripping plate back into its initial or rest position above the actual filter element so that the known solution, especially due to use of the working cylinder, is designed to not only be geometrically large in the axial direction, but also requires additional energy for cleaning or stripping during operation of the respective working cylinder.